This invention relates to an automatic transmission for vehicles which accomplishes non-stage transmission using a double pinion planetary gear.
An automatic transmission for vehicles has been provided which comprises a torque converter and a planetary gear combined with the torque converter. The torque converter increases the torque developed by an engine. However, a range of increase in the torque is so small that the automatic transmission is insufficient to be used singly in automobiles. Accordingly, in the practical use, the automatic transmission is combined with a plurality of planetary gears so that one of a plurality of reduction gear ratios for the planetary gears is automatically selected according to a driving condition.
However, since the reduction gear ratio is stepwise shifted according to the driving condition in the above-described automatic transmission, gear shift during acceleration results in a large shock and momentarily reduces the number of revolution of the engine. As a result, the vehicle cannot smoothly be accelerated. Further, the reduction gear ratio is suddenly increased when the automatic transmission is downshifted according to the operation of an accelerator so that the vehicle is accelerated. As a result, the vehicle body is shaken such that a driver and passengers may feel uncomfortable. Even when the accelerator is returned for deceleration, the automatic transmission is not downshifted but would sometimes be upshifted by contraries. As a result, the engine brake cannot effectively be applied.
Further, the torque converter disadvantageously has a large transmission loss, and in addition, the transmission loss is further increased since a plurality of planetary gears are used. Further, the overall automatic transmission has a complicated structure and is large in size and heavy in weight. Thus, the automatic transmission increases the weight of the vehicle and the size of a driving system thereof. Further, since the planetary gears are controlled by means of oil hydraulics, the loss resulting from production of oil pressure is large. Additionally, the oil pressure control is complicated and accordingly increases the cost and results in failure.
In addition, when a driving force of drive wheels is smaller than the current running resistance of the vehicle, the current number of revolution cannot be maintained or the engine causes knocking which results in uncomfortableness. Further, since the vehicle cannot be accelerated, the automatic transmission is controlled so that such a reduction gear ratio is selected that the vehicle runs under a condition where the driving force of the drive wheels is sufficiently large according to the speed of the vehicle relative to the running resistance. In other words, while the vehicle is running at a constant speed, the reduction gear ratio is larger than an optimum one at which the driving force of the drive wheels equilibrates the current running resistance, whereupon fuel is consumed uselessly.
On the other hand, a belt continuously variable transmission (CVT) utilizing pulleys and a belt has recently been put to practical use. In the belt CVT, the belt couples two pulleys and diameters of both pulleys are changed so that the reduction gear ratio is continuously variable. Accordingly, since non-stage transmission can be accomplished, gear shift results in no shock such that the vehicle can smoothly be accelerated. However, the belt has a low durability in the currently used belt CVT, whereupon it is difficult to apply the current belt CVT to high-powered engines. Further, since the diameters of the pulleys are varied by the oil hydraulics so that the reduction gear ratio is adjusted, an increase rate of the engine speed does not agree with an acceleration rate of the vehicle even though the engine speed is increased according to the operation of the accelerator. This results in a sense of physical disorder and a large loss in the engine revolution for production of oil pressure. Further, the belt which is originally annular is elastically deformed into an elliptic shape when attached to the pulleys. The slippage between the pulleys and the belt or the loss due to the aforesaid deformation is large. Further, the belt CVT results in a delay time between a sudden change of load or engine power and gear shift. As a result, the belt CVT is unsuitable for the sports driving. Further, even though the CVT can accomplish the non-stage transmission, it is controlled so that such a reduction gear ratio is selected that the vehicle runs under a condition where the driving force of the drive wheels is sufficiently large according to the speed of the vehicle relative to the running resistance, as in the same manner in the aforesaid automatic transmission. As a result, fuel is wasted.
On the other hand, no transmission is provided in electric railcars with an electric motor serving as a driving source and electric motorcars. In these vehicles, a motor voltage and a motor current are controlled by an inverter so that the motor torque and speed are controlled according to a running speed of the vehicle. However, the cost for such a control device is extremely high. Further, the control device carries out a control manner in which the driving force of the drive wheels becomes larger than the running resistance of the vehicle so that the vehicle can run smoothly. This results in waste of the electric power. Additionally, since the motor torque and speed are controlled according to the speed of the vehicle, the driving force of the drive wheels would become unsuitable depending upon load applied to the drive wheels or the motor would be overloaded.
Bicycles are provided with a transmission manually shifting a reduction gear ratio. The manual operation is troublesome and the transmission cannot generally be shifted while the bicycle is stopped. Thus, the transmission is not effectively used in the bicycle. Further, wind power generating systems are provided with no transmission. Accordingly, a generator is not rotated when torque due to wind power is smaller than a stationary force of the generator, so that no electric power is produced. Further, when the torque due to wind power is larger than a torque required to maintain the generation in the generator, the torque due to wind power cannot efficiently be transmitted to the generator, whereupon the generating efficiency is low.
Therefore, an object of the present invention is to provide an automatic transmission which has a small size and a simple construction, causes no shock due to gear shift, and can convert input rotation to output rotation at a maximum efficiency with no control.
The present invention provides an automatic transmission comprising an input first rotating member, an output second rotating member provided to be coaxial with the first rotating member, a third rotating member provided to be coaxial with the first rotating member, and a rotation transmitting element provided on the third rotating member to transmit rotation of the first rotating member to the second rotating member so that the second rotating member is rotated at a predetermined reduction ratio exceeding 1 in a direction of rotation of the first rotating member in a stopped state of the third rotating member. The reduction ratio is increased as a difference between rotational speeds of the first and third rotating members is rendered larger. In this construction, the third rotating member is bidirectionally rotatable. The second rotating member is automatically adjusted to a number of revolution at which an equilibrium is maintained between torque developed by the second rotating member and a load applied to the second rotating member when the third rotating member is in rotation at a number of revolution ranging between zero at which the third rotating member is stationary and a number of revolution at which the third rotating member is in rotation together with the first rotating member in one and the same direction.
According to the above-described construction, a force acting upon the third rotating member during rotation of the first rotating member is a resultant force of a first torque acting in the same direction as the first rotating member is rotated due to the fact that the rotation transmitting element provided on the third rotating member tends to rotate with the first rotating member and a second torque acting in the direction opposite to rotation of the first rotating member due to a repulsive force the rotation transmitting element receives from the second rotating member. Accordingly, the third rotating member is rotated in the same direction as the first rotating member is rotated when the first torque is larger than the second torque.
Assume now that the third rotating member is being rotated in the same direction as the first rotating member is being rotated. Under this condition, the second rotating member is rotated in the same direction as the first rotating member as the result of operation of the rotation transmitting element and is pressed by the rotation transmitting element with rotation of the third rotating member. More specifically, two rotation transmission paths are provided between the first and second rotating members, that is, a first transmission path provided by the operation of the rotation transmitting element and having a predetermined reduction ratio larger than 1 and a second transmission path provided by the rotation of the third rotating member and having the reduction ratio of 1. The true speed of the second rotating member is the sum of speeds of the second rotating member rotated via the respective transmission paths. In this case, when the third rotating member is stopped, all the rotation of the first rotating member is consumed for rotation of the second rotating member by the operation of the rotation transmitting element in the same direction as the first rotating member is rotated. Further, when the third rotating member is rotated at the same speed as the first rotating member is rotated, all the rotation of the first rotating member is consumed for the rotation transmitting element pressing the second rotating member in the same direction as the first rotating member is rotated. When the third rotating member is being rotated at a speed lower than that of the first rotating member, one part of rotation of the first rotating member is consumed for rotation of the second rotating member by the operation of the rotation transmitting element in the same direction as the first rotating member is rotated. The other part of the rotation of the first rotating member is consumed for the rotation transmitting element pressing the second rotating member in the same direction as the first rotating member is rotated.
In other words, the number of revolution of the second rotating member is obtained by adding the number of revolution of the third rotating member and a number of revolution obtained by dividing, by a reduction ratio of the automatic transmission with the third rotating member being stopped, the value obtained by subtracting the number of revolution of the third rotating member from the number of revolution of the first rotating member. Furthermore, the reduction ratio of the automatic transmission mechanism at this time is obtained by dividing the number of revolution of the first rotating member by the speed of the second rotating member.
Thus, as the difference between the numbers of revolution of the first and third rotating members becomes large, the rotation at the predetermined reduction ratio larger than 1 is more predominant in the rotation transmitted from the first rotating member to the second rotating member. As a result, since the reduction ratio is increased, the torque developed by the second rotating member is increased although its number of revolution is reduced. Further, as the difference between the numbers of revolution of the first and third rotating members becomes small, the rotation at the reduction ratio of 1 is more predominant in the rotation transmitted from the first rotating member to the second rotating member. As a result, since the reduction ratio is decreased, the torque developed by the second rotating member is decreased although its number of revolution is increased. The aforesaid rotational characteristic of the second rotating member shows that the number of revolution of the second rotating member is automatically adjustable according to the magnitude of a load acting upon the second rotating member on condition that the number of revolution and torque of the first rotating member are constant. Accordingly, the number of revolution of the second rotating member is automatically adjusted so that the torque thereof equilibrates the magnitude of the load.
On the other hand, when the load is increased in the above-mentioned equilibrium state, the repulsive force the second rotating member exerts on the rotation transmitting element provided on the third rotating member is increased and accordingly, the torque rotating the third rotating member in the direction opposite to the direction of the first rotating member is increased, whereas the torque rotating the third rotating member in the same direction as the first rotating member rotates remains unchanged. Consequently, since the number of revolution of the third rotating member is reduced, the difference between the numbers of revolution of the first and third rotating members is rendered larger. In this case, the reduction ratio of the automatic transmission is increased as the difference between the numbers of revolution of the first and third rotating members is rendered larger. Accordingly, the reduction ratio of the automatic transmission is increased according to a reduction in the number of revolution of the third rotating member, whereupon the number of revolution of the second rotating member is reduced. As a result, the number of revolution of the second rotating member is reduced according to an increase in the load acting upon the second rotating member. However, since the torque of the second rotating member is increased with the reduction in the number of revolution thereof, the number of revolution of the second rotating member is reduced until the torque thereof equilibrates the magnitude of the load, being then stabilized.
Further, when the load is reduced in the above-mentioned equilibrium state, the repulsive force the second rotating member exerts on the rotation transmitting element provided on the third rotating member is reduced and accordingly, the torque rotating the third rotating member in the direction opposite to the direction of the first rotating member is increased, whereas the torque rotating the third rotating member in the same direction as the first rotating member rotates remains unchanged. Consequently, since the speed of the third rotating member is increased, the difference between the numbers of revolution of the first and third rotating members is rendered smaller. In this case, the reduction ratio of the automatic transmission is reduced as the difference between the numbers of revolution of the first and third rotating members is rendered smaller. Accordingly, the reduction ratio of the automatic transmission is reduced according to an increase in the number of revolution of the third rotating member, whereupon the number of revolution of the second rotating member is increased. As a result, the number of revolution of the second rotating member is increased according to a reduction in the load acting upon the second rotating member. However, since the torque of the second rotating member is reduced with the increase in the number of revolution thereof, the number of revolution of the second rotating member is increased until the torque thereof equilibrates the magnitude of the load, being then stabilized.
As the result of the above-described operation, the torque of the second rotating member is increased simultaneously with reduction in the number of revolution thereof when the load is increased in the equilibrium state of the torque of the second rotating member and the load. The torque of the second rotating member is reduced simultaneously with increase in the number of revolution thereof when the load is reduced. Thus, the number of revolution of the second rotating member is automatically adjusted so as to equilibrate the magnitude of the load even though the load varies.
On the other hand, when the number of revolution of the first rotating member is reduced in an equilibrium state of the torque of the second rotating member and the load, the torque rotating the rotation transmitting element provided on the third rotating member together with the first rotating member is reduced. Further, the torque acting upon the third rotating member to rotate it in the same direction as the first rotating member is rotated is reduced although the torque acting upon the third rotating member to rotate it in the direction opposite to the direction in which the first rotating member is rotated remains unchanged. Accordingly, the number of revolution of the third rotating member is reduced such that the difference between the numbers of revolution of the first and third rotating members becomes larger. In this case, the reduction ratio of the automatic transmission is increased as the difference between the numbers of revolution of the first and third rotating members becomes larger. Accordingly, the reduction ratio of the automatic transmission is increased according to a reduction in the number of revolution of the third rotating member such that the number of revolution of the second rotating member is reduced. Consequently, the number of revolution of the second rotating member is reduced according to a reduction in the number of revolution of the first rotating member. However, since the torque of the second rotating member is increased with the reduction in the number of revolution thereof, the number of revolution of the second rotating member is reduced until the torque thereof equilibrates the magnitude of the load, being then stabilized.
Further, when the number of revolution of the first rotating member is increased in an equilibrium state of the torque of the second rotating member and the load, the torque rotating the rotation transmitting element provided on the third rotating member together with the first rotating member is increased. Further, the torque acting upon the third rotating member to rotate it in the same direction as the first rotating member is rotated is increased although the torque acting upon the third rotating member to rotate it in the direction opposite to the direction in which the first rotating member is rotated remains unchanged. Accordingly, the number of revolution of the third rotating member is increased such that the difference between the numbers of revolution of the first and third rotating members becomes smaller. In this case, the reduction ratio of the automatic transmission is reduced as the difference between the numbers of revolution of the first and third rotating members becomes smaller. Accordingly, the reduction ratio of the automatic transmission is reduced as the difference in the numbers of revolution of the first and third rotating members becomes small. Accordingly, the reduction ratio of the automatic transmission is reduced according to an increase in the number of revolution of the third rotating member. As a result, the number of revolution of the second rotating member is increased according to an increase in the number of revolution of the first rotating member. However, since the torque of the second rotating member is reduced with the increase in the number of revolution of the second rotating member, the number of revolution of the second rotating member is increased until the torque thereof equilibrates the magnitude of the load, being then stabilized.
As the result of the above-described operation, the torque of the second rotating member is increased simultaneously with the reduction in the number of revolution thereof when the number of revolution of the first rotating member is reduced in the equilibrium state of the torque of the second rotating member and the load. Upon increase in the number of revolution of the first rotating member, the torque of the second rotating member is reduced simultaneously with increase in the number of revolution thereof. Accordingly, the number of revolution of the second rotating member is automatically adjusted so that the torque thereof equilibrates the magnitude of the load, although the number of revolution of the first rotating member varies.
In short, the first, second and third rotating members correspond to a pump impeller, a turbine liner and a stator of a torque converter employed in a conventional vehicle automatic transmission respectively.
The invention also provides an automatic transmission comprising an input first rotating member, an output second rotating member provided to be coaxial with the first rotating member, a third rotating member provided to be coaxial with the first rotating member, and rotation transmitting means provided on the third rotating member to transmit rotation of the first rotating member to the second rotating member so that the second rotating member is rotated at a number of revolution and a reduction ratio shown by following equations respectively in a direction of rotation of the first rotating member:
N2=N3+(N1xe2x88x92N3)/R0
R=N1xc2x7R0/((R0xe2x88x921)xc2x70N3+N1)
where N1 is a number of revolution of the first rotating member, N2 is a number of revolution of the second rotating member, N3 is a number of revolution of the third rotating member, R is a reduction ratio of the automatic transmission, and R0 is a reduction ratio of the automatic transmission in a stopped state of the third rotating member and smaller than 1. In this construction, the third rotating member is bidirectionally rotatable. The second rotating member is automatically adjusted to a number of revolution at which an equilibrium is maintained between torque developed by the second rotating member and a load applied to the second rotating member when the third rotating member is in rotation at a number of revolution ranging between zero at which the third rotating member is stationary and a number of revolution at which the third rotating member is in rotation together with the first rotating member in one and the same direction.
According to the above-described construction, the number of revolution N2 of the second rotating member corresponding to the number of revolution N3 of the third rotating member is represented as the relationship shown in FIG. 3 on condition that the number of revolution N1 of the first rotating member is constant. In FIG. 3, a sun gear, a ring gear and a carrier correspond to the first, second and third rotating members respectively. Further, the reduction ratio R of the automatic transmission corresponding to the number of revolution N3 of the third rotating member is represented as the relationship shown in FIG. 4. When the number of revolution of the third rotating member is small on condition that the number of revolution of the first rotating member is constant, the number of revolution of the second rotating member is small. However, the torque of the second rotating member is large since the reduction ratio is large. Further, when the number of revolution of the third rotating member is large, the number of revolution of the second rotating member is large. However, the torque of the second rotating member is small since the reduction ratio is small. This characteristic means that the torque of the second rotating member is automatically adjusted so that the number of revolution thereof equilibrates the magnitude of the load.
Each aforesaid automatic transmission preferably further comprises a reverse rotation preventing element which prevents the third rotating member from rotation in a direction opposite one in which the first rotating member is rotated. In each aforesaid construction, a repulsive force the rotation transmitting element provided on the third rotating member receives from the second rotating member is large when the load is large. As a result, the third rotating member is rotated in the direction opposed to the first rotating member, whereupon rotation of the first rotating member cannot be transmitted to the second rotating member. In this case, however, the reverse rotation preventing element prevents the third rotating member from rotation in the direction opposed to the first rotating member, so that the rotation of the first rotating member is transmitted to the second rotating member.
The load acting upon the second rotating member is reduced upon increase in the number of revolution thereof. Accordingly, the repulsive force the rotation transmitting element receives from the second rotating member is rendered small. Consequently, since the third rotating member is rotated in the same direction as the first rotating member, the torque of the second rotating member is automatically adjusted so that the number of revolution thereof equilibrates the magnitude of the load. In short, the reverse rotation preventing element corresponds to a one-way clutch provided for limiting a rotational direction of the stator of the torque converter employed in the conventional vehicle automatic transmission.
Each aforesaid automatic transmission preferably further comprises a fourth rotating member, a reverse rotation transmitting element which transmits rotation of the third rotating member to the fourth rotating member under a condition where the third rotating member is being rotated in a direction opposite one in which the first rotating member is rotated, and a stopping element which applies a stopping force to the fourth rotating member. In each aforesaid construction, a repulsive force the rotation transmitting element provided on the third rotating member receives from the second rotating member is large when the load is large. As a result, the third rotating member is rotated in the direction opposed to the first rotating member, whereupon rotation of the first rotating member cannot be transmitted to the second rotating member. In this case, however, the reverse rotation preventing element transmits the rotation of the third rotating member to the fourth rotating member, so that the fourth rotating member is rotated. When the stopping element is then operated, a stopping force is applied to the fourth and accordingly third rotating members, so that the rotation of the first rotating member is transmitted to the second rotating member.
The load acting upon the second rotating member is reduced upon increase in the number of revolution thereof. Accordingly, the repulsive force the rotation transmitting element receives from the second rotating member is rendered small. Consequently, since the third rotating member is rotated in the same direction as the first rotating member, the torque of the second rotating member is automatically adjusted so that the number of revolution thereof equilibrates the magnitude of the load. In short, the stopping element functions as a clutch element for transmitting rotation of the first rotating member to the second rotating member. The above-described construction is suitable for a case where a rotating source which rotates the first rotating member is an internal combustion engine or a case where a starting torque is large as in large-sized electric motors such that a large torque acts in the starting.
The stopping element preferably increases the stopping force applied to the fourth rotating member with increase in a number of revolution of the fourth rotating member. The fourth rotating member is rotated when a large load rotates the third rotating member in the direction opposed to the first rotating member. Accordingly, the stopping element increases its stopping force against the fourth rotating member as the number of revolution of the fourth rotating member is increased. Upon stop of the third rotating member, the rotation transmitting element is operated so that the rotation of the first rotating member is transmitted to the second rotating member, whereupon the second rotating member is rotated in the same direction as the first rotating member. Since the rotation transmitting element provided on the third rotating member tends to rotate with the first rotating member, the third rotating member is subjected to a first torque which rotates it in the same direction as the first rotating member. Further, the rotation transmitting element receives a repulsive force from the second rotating member. The repulsive force applies to the third rotating member a second torque which rotates it in the direction opposed to the first rotating member. In this case, the repulsive force the rotation transmitting element receives from the second rotating member is large when the second rotating member starts to rotate in the same direction as the first rotating member. Accordingly, the second torque is larger than the first torque such that the third rotating member is rotated in the direction opposed to the first rotating member. When the number of revolution of the second rotating member is increased and the torque acting upon the second rotating member is reduced, the repulsive force the rotation transmitting element receives from the second rotating member is reduced. As a result, the first torque acting upon the third rotating member is increased such that the number of revolution at which the third rotating member is rotated in the direction opposed to the first rotating member is reduced. Consequently, since the number of revolution of the fourth rotating member is reduced, the stopping force the stopping element applies to the third rotating member is reduced. That is, the stopping element applies the stopping force to the third rotating member but does not completely stop it. In short, the stopping element functions as a clutch element for transmitting the rotation of the first rotating member to the second rotating member in an incompletely or half engaged state.
The stopping element preferably increases the stopping force applied to the fourth rotating member with increase in a number of revolution of the first rotating member. The fourth rotating member is rotated when a large load rotates the third rotating member in the direction opposed to the first rotating member. At this time, the stopping element increases its stopping force against the fourth rotating member as the number of revolution of the first rotating member is increased. Upon stop of the third rotating member, the rotation transmitting element is operated so that the rotation of the first rotating member is transmitted to the second rotating member, whereupon the second rotating member is rotated in the same direction as the first rotating member. In this case, the number of revolution of the third rotating member and accordingly the number of revolution of the fourth rotating member are large when the number of revolution of the first rotating member is large. Accordingly, although the stopping element increases its stopping force against the fourth rotating member as the number of revolution of the first rotating member is increased, the third rotating member is not completely stopped. In short, the stopping element functions as a clutch element for transmitting the rotation of the first rotating member to the second rotating member in an incompletely or half engaged state.
The stopping element preferably applies the stopping force to the fourth rotating member when externally operated. When externally operated, the stopping element stops the fourth rotating member and accordingly the third rotating member. Consequently, the rotation of the first rotating member can be transmitted to the second rotating element. In short, the stopping element functions as manual clutch means.
Further, the automatic transmission preferably further comprises a stop holding element which holds the third rotating member in a stopped state. When the stop holding element is operated so that the third rotating member is held in the stopped state, rotation of the first rotating member can be transmitted to the second rotating member at the predetermined reduction ratio exceeding 1. Accordingly, the rotation of the first rotating member can be transmitted to the second rotating member irrespective of the direction of rotation of the first rotating member. The above-described construction is suitable for electric vehicles and trains in which the rotational direction of the rotating source rotating the first rotating member is reversible.
The stop holding element preferably reduces a stop holding force with increase in the number of revolution of the second rotating member rotated in a same direction as the first rotating member is rotated. The stopping element reduces the stopping force against the third rotating member when the number of revolution of the second rotating member is increased. Accordingly, the third rotating member is rotated in the same direction as the first rotating member and the number of revolution of the second rotating member is automatically adjusted so that the torque thereof equilibrates the load. In this case, since the foregoing is applied to a case where the first rotating member is rotated in the reverse direction, the rotation of the first rotating member can be transmitted to the second rotating member irrespective of the rotational direction of the first rotating member.
The stop holding element preferably releases the third rotating member from a stop holding force applied thereto when the number of revolution of the second rotating member rotated with the first rotating member in a same direction as the first rotating member is rotated has exceeded a predetermined number of revolution. When the number of revolution of the second rotating member rotated in the same direction as the first rotating member is increased to or above a predetermined value, the torque rotating the third rotating member in the same direction as the first rotating member can be considered to be larger than the torque rotating the third rotating member in the direction opposed to the first rotating member. Accordingly, the third rotating member is rotated in the same direction as the first rotating member even though the stop holding element releases the third rotating member from the stop holding force. Consequently, the number of revolution of the second rotating member is automatically adjusted so that the torque thereof equilibrates the magnitude of the load. In this case, since the foregoing is applied to a case where the first rotating member is rotated in the reverse direction, the rotation of the first rotating member can be transmitted to the second rotating member irrespective of the rotational direction of the first rotating member.
The automatic transmission preferably further comprises a detecting element which detects torque rotating the third rotating member in a same direction as the first rotating member is rotated. In this construction, the stop holding element releases the third rotating member from a stop holding force applied thereto when the detecting element detects the torque rotating the third rotating member in the same direction as the first rotating member is rotated. When the third rotating member is subjected to torque tending to rotate it in the same direction as the first rotating member during rotation of the latter, the detecting element detects that. Since the stop holding element then releases the third rotating member from the stop holding force, the third rotating member is rotated in the same direction as the first rotating member and the number of revolution of the second rotating member is automatically adjusted so that the torque thereof equilibrates the magnitude of the load. In this case, since the foregoing is applied to a case where the first rotating member is rotated in the reverse direction, the rotation of the first rotating member can be transmitted to the second rotating member irrespective of the direction of rotation of the first rotating member.
Further, the automatic transmission preferably further comprises a number-of-revolution controlling element which controls a number of revolution of the third rotating member. The torque of the second rotating member is increased more as the difference between the numbers of revolution of the first and third rotating members becomes large. Accordingly, the torque of the second rotating member can be adjusted to any value when the number of revolution of the third rotating member is controlled by the number of revolution controlling element.
The number-of-revolution controlling element preferably combines a force stopping the third rotating member and a force integrating the third rotating member with the first rotating member, thereby controlling the number of revolution of the third rotating member. The force stopping the third rotating member is caused to work when the number of revolution of the third rotating member is to be reduced, whereas the force integrating the third rotating member with the first rotating member when the number of revolution of the third rotating member is to be increased. Consequently, the number of revolution of the third rotating member can be controlled by a simple construction.
The number-of-revolution controlling element preferably carries out the operation of the reverse rotation preventing element. The number of revolution of the third rotating member is reduced by the number-of-revolution controlling element when the load is so large that the third rotating member is rotated in the direction opposed to the first rotating member. As a result, in the construction including the number-of-revolution controlling element, the rotation of the first rotating member can be transmitted to the second rotating member without using a reverse rotation limiting element.
The number-of-revolution controlling element preferably carries out an operation of the stop holding element. In the construction including the number-of-revolution controlling element, the third rotating member is held in the stopped state by the number-of-revolution controlling element, whereupon the rotation of the first rotating member can be transmitted to the second rotating member without using a stop holding element irrespective of the direction of rotation of the first rotating member.
The automatic transmission preferably further comprises a load determining element which determines a magnitude of load based on a difference between numbers of revolution of the first and third rotating members both rotated in a same direction. In a case where the third rotating member is rotated in the same direction as the first rotating member, the difference between the numbers of revolution of the first and third rotating members is large when the load is large. The difference is small when the load is small. Accordingly, the load determining element can determine the magnitude of the load on the basis of the difference between the number of revolution of the first rotating member and the number of revolution of the third rotating member rotated in the same direction as the first rotating member.
The automatic transmission preferably includes a pair of the aforesaid automatic transmissions including the respective reverse rotation preventing elements and having effective input rotational directions opposed to each other. The automatic transmission further comprises an input rotation transmitting element transmitting input rotation only to the first rotating member of the automatic transmission effectively operating with respect to the direction of input rotation, and an output rotation transmitting element transmitting as an output rotation only rotation of the second rotating member of the automatic transmission effectively operating with respect to the input rotation.
According to the above-described construction, the input rotation transmitting element effectively transmits input rotation to the first rotating member of one of the paired automatic transmissions but does not effectively transmit the input rotation to the first rotating member of the other automatic transmission. In said one automatic transmission, the reverse rotation preventing element prevents the third rotating member from being rotated in the direction opposed to the first rotating member. Accordingly, the rotation of the first rotating member is transmitted to the second rotating element. Consequently, only said one automatic transmission effectively operates, and the third rotating member is rotated in the same direction as the first rotating member, so that the number of revolution of the second rotating member is automatically adjusted so that the torque thereof equilibrates the magnitude of the torque. In this case, since said one automatic transmission is effectively operated, the output rotation transmitting element effectively transmits the rotation of the second rotating member of said one automatic transmission is effectively transmitted as the output rotation.
Further, when rotated in the reverse direction, the input rotation is effectively transmitted by the input rotation transmitting element to the first rotating member of said one transmitting element but is not effectively transmitted to the first rotating member of said other automatic transmission. Consequently, only said other automatic transmission effectively operates and the rotation of the second rotating member of said other automatic transmission can effectively be transmitted. The above-described construction is suitable for the construction in which reverse rotation is possible in the input rotation.
The first rotating member preferably comprises a sun gear of a double pinion planetary gear, the second rotating member preferably comprises a ring gear of the planetary gear, the third rotating member preferably comprises a planetary pinion carrier of the planetary gear, and the rotation transmitting element preferably comprises a pinion gear of the planetary gear. Since the double pinion planetary gear is used, the size of the automatic transmission can be reduced and the construction thereof can be simplified.
The reverse rotation preventing element preferably comprises a one-way clutch. Consequently, the construction of the reverse rotation preventing element can be simplified.
The reverse rotation transmitting element preferably comprises a one-way clutch. Consequently, the construction of the reverse rotation transmitting element can be simplified.
A plurality of the automatic transmissions are preferably serially connected to each other or one another. The reduction ratio of the overall automatic transmission is obtained by multiplication of reduction ratios of the respective automatic transmissions. Consequently, a large reduction ratio can be obtained.
The automatic transmission is preferably connected to a step-up gear with a reduction ratio smaller than 1. Consequently, the minimum reduction ratio can be set at a value smaller than 1.
A plurality of the automatic transmissions are preferably provided and rotation of the second rotating members of the respective automatic transmissions are combined together to be delivered. In order that the numbers of revolution of a plurality of rotating members may efficiently be combined together, the numbers of revolution of all the rotating members should be equal to each other or one another. When the numbers of revolution of the rotating members differ from each other, a rotating member with a small number of revolution becomes a resistance against a rotating member with a large number of revolution, so that the overall transmission efficiency is reduced.
In the above-described construction, however, the reduction ratio of each automatic transmission is automatically adjusted individually according to the magnitude of the load. Consequently, the rotation of the second rotating members can be combined at a maximum efficiency to be delivered even when the numbers of revolution of the first rotating members of the respective automatic transmissions differ from one another.
A plurality of the automatic transmissions are preferably provided. The first rotating members are rotated by a rotating source and the drive wheels are rotated by the second rotating members respectively. In the acceleration, the reduction ratio is smoothly reduced as the vehicle number of revolution is increased. Accordingly, the vehicle can smoothly be accelerated without shock due to gear shift. Further, in the deceleration, the reduction ratio is smoothly increased as the speed of the vehicle is reduced. Accordingly, since the rotating source can serve as a brake, the vehicle can smoothly be decelerated without shock due to gear shift. Further, since the rotation of the rotating source is transmitted to the drive wheels at a maximum efficiency, fuel consumption can be improved when the rotating source is an engine. The consumption of a battery can be reduced when the rotating source is an electric motor used in hybrid cars or electric cars.
The number-of-revolution controlling element preferably reduces the number of revolution of the third rotating member when a braking operation is carried out. In this construction, the number-of-revolution controlling element reduces the number of revolution of the third rotating member when a braking operation is carried out so that the vehicle is decelerated. Consequently, since the reduction ratio is increased, a large braking force can be obtained.
In the aforesaid construction that the number-of-revolution controlling element reduces the number of revolution of the third rotating member when a braking operation is carried out, the reduction in the number of revolution of the third rotating member increases the reduction ratio. As a result, the number of revolution of the first rotating member and accordingly the number of revolution of the rotating source sometimes exceed respective allowed numbers of revolution. This would result in malfunction of the rotating source. In view of this problem, the number-of-revolution controlling element preferably controls the number of revolution of the third rotating member so that a number of revolution of the rotating source is reduced to or below an allowed number of revolution. Consequently, the number of revolution of the rotating member can be prevented from exceeding the allowed number of revolution.
The automatic transmission preferably further comprises an auxiliary rotating source for rotating the second rotating member in a same direction as the first rotating member is rotated, the auxiliary rotating source being operated on the basis of the magnitude of load determined by the load determining element. The auxiliary rotating source is operated on the basis of the magnitude of load determined by the load determining element, whereby the torque of the second rotating member and accordingly the torque of the drive wheels can be adjusted optionally.
A rotating force the auxiliary rotating source applies to the second rotating member is preferably increased with an increase in the load determined by the load determining element. The number of revolution of the second rotating member and accordingly the number of revolution of the drive wheels are reduced when the load is increased such that the number of revolution of the third rotating member is reduced. In the above-described construction, when the number of revolution of the third rotating member has been reduced, the load determining element determines that the load has been increased. Accordingly, the auxiliary rotating source increases the torque which rotates the second rotating member in the same direction as the first rotating member. Consequently, the number of revolution of the second rotating member and accordingly the number of revolution of the drive wheels can be prevented from being reduced. The aforesaid construction is suitable for hybrid cars and motor-assisted bicycles.
The automatic transmission is preferably provided for every drive wheel. Each automatic transmission automatically adjusts the number of revolution of the corresponding drive wheel individually so that the driving force equilibrates the running resistance. Accordingly, the number of revolution of each inner drive wheel becomes smaller than that of each outer drive wheel when the vehicle turns. Consequently, the vehicle can turn without an excessive force being applied to each drive wheel. That is, the automatic transmission can function as a differential gear.
Further, the rotation of the rotating source is transmitted to each drive wheel individually in the above-described construction. Accordingly, even when one of the drive wheels slips, the driving force of each of the other drive wheels is not lost. Thus, the automatic transmission can function as a non-slip differential gear. Further, the number of revolution of the slipped drive wheel is rapidly increased such that the driving force is rapidly reduced. Consequently, slippage can promptly be eliminated.